1. Field of the Invention
The present invention is directed to hydrocarbon hydroconversion processes, and more particularly, to reforming processes. Still more particularly, the present invention is concerned with a catalytic composition and a process for the hydroconversion of hydrocarbons in the presence of the catalytic composition. The catalyst comprises a platinum group component and a Group IIB component, preferably zinc or cadmium, in association with a porous solid carrier. The catalyst may advantageously also comprise 0.01 to 3 weight percent of a second catalyst component, preferably selected from the group consisting of a rhenium component, a tin component, a germanium component, and a lead component.
2. Prior Art
Hydrocarbon hydroconversion processes, such as hydrocracking, hydrogenation, hydrofining, isomerization, alkylation, desulfurization and reforming, are of special importance in the petroleum industry as a means for improving the quality and usefulness of hydrocarbons. The requirement for a diversity of hydrocarbon products, including, for example, high quality gasoline, has led to the development of many catalysts and procedures for converting hydrocarbons in the presence of hydrogen to useful products. A particularly important hydrocarbon hydroconversion process is reforming. Although many features of the present invention are discussed in terms of reforming, it is to be understood that the present invention relates to other hydrocarbon hydroconversion processes as well.
In the development of catalysts for catalytic hydroconversion processes, it is important that the catalyst exhibit not only the capability to initially perform the specified functions but also that it has the capability to perform satisfactorily for prolonged periods of time. Thus, in the development of new catalysts, attention must be directed to the activity, selectivity, and stability characteristics of the catalyst. The activity of a catalyst is a measure of the catalyst's ability to convert hydrocarbon reactants to products at a specified severity level, i.e., at a particular temperature, pressure, hydrogen-to-hydrocarbon mole ratio, etc. The selectivity of the catalyst refers to the ability of the catalyst to produce high yields of desirable products, and accordingly low yields of undesirable products. The stability of a catalyst is a measure of the ability of the catalyst to maintain the activity and selectivity characteristics over a specified period of time. Thus, for example, a catalyst for successful reforming must possess good selectivity, i.e., be able to produce high yields of high octane number gasoline products and accordingly low yields of light hydrocarbon gases. The catalyst should also possess good activity in order that the temperature required to produce a certain quality product need not be too high. Also, the high stability is desired so that the activity and selectivity characteristics can be retained during prolonged periods of reforming operation. Thus, the temperature stability, which is generally referred to as the fouling rate of the catalyst, desirably is such that the temperature need not be raised at a high rate in order to maintain conversion of the feed to a constant octane product. Also, the yield stability of the catalyst desirably is such that the amount of valuable C.sub.5 + gasoline products does not decrease appreciably during prolonged operation at a constant conversion.
As indicated above, the present invention is particularly concerned with catalytic reforming, that is, the treatment of naphtha fractions or feeds to improve the octane rating. Catalytic reforming operations are characterized by employing catalysts which selectively promote such hydrocarbon reactions as dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to naphthenes and aromatics, isomerization of normal paraffins to isoparaffins, and hydrocracking of relatively long-chained paraffins. Most catalysts used in reforming processes comprise platinum group components, particularly platinum, in association with porous solid carriers, for example, alumina. Research efforts have been expended to seek substitutes for platinum and/or to seek catalytic promoters to use with platinum catalysts to increase their activity, stability and selectivity characteristics.
For example, U.S. Pat. No. 3,415,737 is the recent basic patent directed to the use of platinum-rhenium catalysts for catalytic reforming, particularly reforming of low sulfur content naphtha feedstocks. Use of the platinum-rhenium catalyst (specifically platinum-rhenium-inorganic support-halide) of U.S. Pat. No. 3,415,737 has been found to result in improved yield stability and fouling rate stability compared to that achieved with platinum catalysts containing no rhenium.
That is, the decline in C.sub.5 + liquid yield of a product of given high octane is lower than with the non-rhenium catalyst as a function of time, and also the increase in temperature in order to maintain a given high octane for the C.sub.5 + product as the on-stream time progresses is lower than with the non-rhenium catalyst. The discovery of a platinum-rhenium catalyst for reforming low sulfur naphthas was thus regarded as an advance of major significance by the petroleum industry and as the most important development in the catalytic reforming field in the last 20 years or so; i.e., since reforming with a platinum-alumina catalyst was first introduced into the petroleum industry in place of the previously used molybdenum-alumina type catalysts; see "New Reforming Catalyst Features Improved Stability, High Yields" by D. H. Stormont, Oil and Gas Journal, Apr. 28, 1969, pages 63-65.
In view of the long time between the platinum-alumina and the improved platinum-rhenium-alumina reforming process, and the difficulty that laid between the basic platinum-alumina catalyst and finding a significantly improved new catalyst, namely the platinum-rhenium-alumina catalyst and its particular manner of use, it would indeed be unexpected to find still further improvements in catalytic reforming processes due to still further improved catalysts. However, the subject of the present invention is a further improvement in catalytic reforming due to an improved catalyst.
Before referring particularly to the present invention, two more relevant areas of prior art might be mentioned, namely use of platinum-germanium catalysts for catalytic reforming and art involving use of catalysts containing Group IIB components such as zinc.
U.S. Pat. No. 2,784,147 is directed to a reforming process using an alumina chromium oxide catalyst containing either germanium oxide, indium oxide or gallium oxide.
U.S. Pat. No. 2,906,701 is directed to a process for the reforming of hydrocarbons with catalysts comprising a support and a "solid solution" comprising germanium and a metal such as platinum. In U.S. Pat. No. 2,906,701 it is stated in Col. 3 that the exact state of the germanium is not known but that the germanium and platinum should be coreduced.
U.S. Pat. No. 3,578,584 is also directed to the use of reforming using a catalyst containing platinum and germanium, and according to Example 1 in U.S. Pat. No. 3,578,584 the catalyst is produced by a procedure involving coreduction of the platinum and germanium.
In all of the latter mentioned patents concerning germanium, there is no Group IIB metal such as zinc in the catalyst.
Referring now to some relevant art concerning zinc, U.S. Pat. No. 2,728,713 discloses a reforming catalyst comprising platinum on a base which is approximately equal molar zinc oxide and alumina oxide, for example, 30 to 50 weight percent zinc oxide. Thus, the zinc oxide is a portion of the base for the catalyst rather than being an added metal as in the case of platinum or other metals which might be added to the catalyst in the range of a few percent, say up to 5 percent or so. The zinc oxide-alumina oxide base is referred to as a zinc aluminate or as a zinc alumina spinel base. The formula for zinc alumina spinel is ZnOAl.sub.2 O.sub.3, so that the amount of zinc is about 35 percent by weight of the support. Thus, U.S. Pat. No. 2,728,713 is not directed to using small amounts of zinc in the reforming catalyst.
In a series of patents assigned to Kellogg Co., such as U.S. Pat. No. 2,743,215, there is described catalysts which are prepared by methods comprising adding a Group IIB metal such as mercury to an aluminum sol, and ultimately volatilizing the Group IIB metal such as mercury out of the catalyst. Thus, the mercury is an agent in the catalyst preparation rather than a component of the final catalyst. The mercury is sometimes referred to as a promoting agent, but it could more properly be referred to as a treating agent. Thus it is stated in the patent that it is preferred that the promoting agent volatilize from the catalyst mass at or before calcination temperatures, and that in some instances the promoting agent is not volatilized at such temperatures, consequently the calcination operation may be conducted under sub-stmospheric pressures in order to remove substantially all of the promoting agent from the catalyst mass.
Example 1 of U.S. Pat. No. 2,743,215 illustrates the preparation method: a solution containing aluminum and mercury is prepared, a solution containing platinum is added, the mixture is then dried and then calcined at 1000.degree. F. The finished catalyst is free of Group IIB component, that is, free of mercury in this instance.
Group IIB metals such as zinc have been disclosed for use in dehydrogenation catalysts, in Netherlands applications Ser. Nos. 6908540 and 7008386. Netherlands Ser. No. 6908540 discloses dehydrogenation catalysts containing Group VIIIB, e.g., platinum; and/or Group VIIB, e.g., rhenium; and Group IIB, e.g., zinc; and preferably an alkali component such as sodium. The actual examples in Netherlands Ser. No. 6908540 are of (a) dehydrogenation catalysts containing platinum plus Group IIB, and (b) dehydrogenation catalysts containing rhenium plus Group IIB. Netherlands Ser. No. 7008386 discloses dehydrogenation catalysts containing Group VIIIB, e.g., platinum, and Group IIB, e.g., plus zinc and preferably an alkali component such as sodium.